Dr Karina J Linnell - Research projects

Seeing with our hands

(co-supervised by Professor Jules Davidoff)

Judgements of the size of a central object are influenced by the size of surround objects such that, the larger the surround objects, the smaller the central circle is perceived to be. However, this perceptual distortion does not impair our actions: when we reach out to grasp the central object, we shape our hands to match the real, and not the perceived, size of the object (see Carey, 2001). We have recently acquired data from a remote African tribe called the Himba showing that their perceptions of size are considerably less distorted than ours. The purpose of this project is to ask whether the unique accuracy of the Himba’s perception stems from a greater facility at ‘seeing with their hands’.

References

Carey, D.P. (2001). Do action systems resist visual illusions? Trends in Cognitive Science, 5, 109-113.

The development of the global bias in westerners

(co-supervised by Professor Jules Davidoff)

Our tendency to perceive global structure (or to see the ‘forest before the trees’) is well documented (Navon, 1977). Limited cross-cultural work (e.g., Rivers, 1905) replicated in our lab (Davidoff et al, 2008) suggests that this global bias is however less strong in remote peoples. Developmental work has suggested that it is also less strong in Western children than in Western adults but reports do not agree about when the global bias develops. This PhD will examine the developmental trajectory of the global bias in Western children and teenagers with a view to understanding the origins of the Western global bias and cultural differences.

References

Davidoff, J., Fonteneau, E. & Fagot, J. (2008). Local and global processing: observations from a remote culture. Cognition, 108, 702-709

Navon, D. (1977). Forest before trees: Precedence of global perception in visual perception.
Cognitive Psychology, 9, 353-383.

Rivers, W.H.R. (1905). Observations on the senses of the Todas. British Journal of Psychology, 1, 321-396.

The Role of Attention in Stereoscopic Perception

(co-supervised by Dr Jan de Fockert)

The visual awareness of stereoscopic, or three-dimensional (3D) depth depends on the successful fusion of the retinal images from the two eyes. Although the computational process of this form of depth perception has been investigated in detail, little is known about the extent to which visual attention plays a role in it. Attention has been shown to affect even very basic aspects of visual processing, such as motion, and this project aims to investigate whether the perception of a 3D image can also be modulated by whether or not it receives attention. Stereoscopic images will be presented alongside a visual task for which the attentional load will be varied in order to manipulate the amount of attention that can be allocated to the 3D image. If 3D perception requires attention, then the perception of the 3D images is expected to vary as a function of attentional load. This effect can be tested for two types of attentional load, perceptual and cognitive load, which previous work suggests may have different effects on 3D perception. Finally, the neural correlates of successful construction of a 3D percept can be investigated using electro-encephalography.

Reach out and grasp: Action and perception in dynamic interaction

with Dr José Van Velzen

We effortlessly and skilfully handle objects in daily life and yet reaching for an object in order to grab it requires a coordinated action taking into account the current position of the thumb and index finger, as well as the location of the object part to be grasped. Attention appears to play a major role in this process by focusing ahead of the movement on the intended end-locations of both finger and thumb (Deubel and Schneider, 2005; Linnell et al, 2005), although recent ERP studies suggest that the location of the hand involved is also attended (Eimer et al, 2005, 2006). In the current project, we will compare the extent to which finger, thumb and grasp object locations are attended, also depending on the ‘graspability’ of the object at finger and thumb locations.

Spatial attention will be ‘probed’ during movement planning and execution stages by presenting (i) tactile and visual stimuli to the finger and thumb and (ii) visual stimuli at intended grasp locations. Attention to tactile and visual probes will be indexed by behavioural report and by the amplitude of the electro-physiological (ERP) responses that they induce. The project will be a collaboration with Dr Linnell and Dr Van Velzen, both of whom work in attention and action, one from a behavioural, and the other from an electrophysiological (ERP), perspective.

References

Linnell, K.J., Humphreys, G.W., McIntyre, D.B., Laitinen, S. & Wing, A.M. (2005). Action modulates object-based selection. Vision Research, 45, 2268-2286.

Eimer, M. & Van Velzen, J. (2006). Covert manual response preparation triggers attentional modulations of visual but not auditory processing. Clinical Neurophysiololgy, 117(5), 1063-74.

Eimer, M., Forster, B., Van Velzen, J. & Prabhu (2005). Covert manual response preparation triggers attentional shifts: ERP evidence for the premotor theory of attention. Neuropsychologia, 43(6), 957-66.

Do spatial and temporal attention interact at perceptual and central levels?

This project has arisen out of an ESRC grant held by Dr Karina Linnell that is just drawing to a close.

Imagine yourself in a crowded train station intent on spotting your friend emerging from a ticket barrier. But there are several ticket barriers, your friend could appear at a number of them, and people are exiting them at a very fast rate. To locate your friend, you must pay attention both to his spatial location and to the time at which he appears. Spatial attention has been studied by scientists for many years and there is now a good consensus on the network of brain areas in the frontal and parietal lobes that control our ability to attend in space. Less work has focused on the neural basis of temporal attention, but there is some evidence that similar brain areas are involved. Given this overlap in the brain areas involved in spatial and temporal attention, we predict that when someone has to attend both to the location of a stimulus and to the time at which it will occur, he will perform worse than when he has only to attend to the location (or only to the time).

To test this, participants in our experiments will have to detect a letter target (which is analogous to you detecting your friend in the train station scenario) on a computer screen. The target will occur in one of two locations, and will appear only very briefly, amongst a rapid stream of other distracting letters (analogous to the rapid stream of people exiting the ticket gates). We will manipulate the spatial and temporal distraction and measure how well participants detect and process the same target both in space and in time as we make these manipulations. In this way, we will be able to judge whether spatial and temporal attention interact, that is, whether there is a cost to attending simultaneously in space and in time.

The project will begin with behavioural investigations of normal healthy volunteers. Depending upon the inclinations of the applicant, these investigations can be extended by ERP studies. If you are interested in further details, please contact Karina Linnell for a full research proposal and reference list.